The long-term objective is to understand the sequential events in the replication of the RNA of a RNA tumor virus, defining and characterizing virus-specific and host cell-derived enzymes and factors that interact with the RNA and its intermediates in replication. More specifically, we initially propose to define and compare the subunit properties of avian and mammalian tumor virus RNA-directed DNA polymerase. We will a) isolate the DNA polymerase subunits of avian myeloblastosis virus, b) localize the DNA polymerase and ribonuclease H activities, c) determine by in vitro reconstitution experiments, the function of each subunit polypeptide in RNA-directed DNA synthesis. Furthermore, we will a) attempt isolation or reconstitution of a DNA polymerase complex from a mammalian RNA tumor virus that has the properties of the two-polypeptide complex of avian myeloblastosis virus, including RNA-directed DNA synthesis; and b) further purify and characterize a RNA-directed DNA polymerase of RNA tumor virus-like particles from human HeLa cells.